Integrated circuit devices comprise many circuit elements arranged compactly in a single physical structure (a "chip"). When operating, these chips tend to generate heat in the course of processing electrical signals. The amount of heat generated by an integrated circuit is dependent on several factors, including the density of circuit elements on the chip, the signal switching speed and the signal power. Chips used in, for example, computers and embedded systems, are likely to generate large amounts of heat, because such integrated circuits generally comprise a very large number of circuit elements arranged on a single chip and are generally operated at high signal switching speeds. Examples of such devices are central processing unit (CPU) chips (such as "microprocessors" or "coprocessors"), memory chips, system control chips (also known as "chipsets"), and others. Excessive heat can degrade performance of these devices, as well as result in permanent physical damage which may cause the chip to fail completely.
Microprocessors have been found to be particularly prone to overheating problems, as microprocessors generally comprise the highest densities of circuit elements and are operated at the highest switching speeds. As a result, microprocessors are typically used in conjunction with a "heat sink" or "cooling fan" to help dissipate the heat generated by the chip. Other integrated circuits have likewise been used in conjunction with heat sinks or cooling fans for similar purposes.
These heat dissipation steps, however, may not be sufficient to completely counteract the heat generated by the device, particularly as the density of circuit elements in integrated circuits and the speed at which integrated circuits are operated continues to increase. Furthermore, the ambient temperature of the surrounding environment may be such that the cooling measures implemented (such as heat sinks) are inadequate. In such instances, it is desirable to avoid catastrophic failure of the chip by taking more active measures, for example, by placing the device in a low power mode, reducing clock speed or shutting down the device completely. In previous systems, for example, microprocessors have been used in conjunction with thermal monitoring systems that cause certain actions to be taken (e.g., clock "throttling" or shut down) once a critical temperature has been sensed.
In the area of, for example, computer design, microprocessor "modules" have been developed that incorporate a microprocessor chip, cache memory chip(s) and system chipset chip(s) on a single printed circuit board. FIG. 1 illustrates a hypothetical arrangement of these components for such a microprocessor module. Printed circuit board 1 includes a microprocessor 2 with heat sink 6, a system chipset 3 (indicated by the dashed line) and one or more cache chips 4. The system chipset 3 comprises one or more integrated circuit chips including, for example, a system controller device 7. A thermal sensor 5 is provided adjacent to microprocessor 2. In particular, thermal sensor 5 is coupled to electrical ground connections for microprocessor 2, such that heat generated by microprocessor 2 may be sensed by thermal sensor 5 via an ambient heat sensing capability (see FIG. 2).
In previous designs, the non-microprocessor chips (the chipset 3 and the cache chips 4) were unlikely to experience heat problems. However, as the circuit density and speed of non-microprocessor chips have increased, and as non-microprocessor chips have been located in closer proximity to the microprocessor (particularly as part of a microprocessor module), these non-microprocessor chips have become prone to heat problems in a similar manner as the microprocessor 2. For example, as shown in FIG. 1, the system controller 7 of chipset 3 may be located in close proximity to microprocessor 2 on the microprocessor module, such that heat generated by microprocessor 2 becomes "coupled" to system controller 7 and contributes to the overall temperature of system controller 7.
Previous responses to similar heat problems in other "thermally critical" devices have been to implement a second thermal sensor proximate to the device. However, the use of an additional thermal sensor in the microprocessor module would not only increase the cost of the module, but also increase the complexity of the design, as multiple thermal sensors must now be controlled and located proximate to the devices to be sensed. Thus, there is a need to monitor the thermal characteristics of multiple integrated circuit chips in a simple and cost effective manner.